Presently, various forms of disk drives have been used in information processors such as computers, etc. Among the disk drives, the disk drive for driving optical disks is required to drive various kinds of optical disks such as a compact disk (hereinafter referred to as a CD), a digital versatile disk (hereinafter referred to as a DVD), etc.
There are cases where the DVD, because of its high recording density and reading and writing rates, is used as a DVD player, which uses a DVD such as a DVD-Video, a DVD-Audio, etc., or storage means such as a DVD-RAM, a DVD-ROM, DVD-RW, etc. There are provided applications at various access speeds and drive speeds.
In conventional optical disk drives, in order to meet the above-mentioned various drive speeds, an initialization drive speed, for example, can be set in three modes: a high performance mode, a normal mode, and a silent mode. For instance, in the high performance mode, the disk drive is always driven at the high drive speed of the drive speeds provided in the disk drive, for example, the 8-time speed. In the normal mode, the disk drive is set so that it is driven at the high speed when accessed and that it is driven at low speed if there is no access within a predetermined time. In the silent mode, the disk drive is set so that it is always driven at a low speed, such as a 1-time drive speed and a 2-time drive speed.
If the disk drive is initialized in the high performance mode or normal mode, read and write operations can be satisfactorily performed regardless of the format in which blocks of data bytes are recorded along a track. However, there will arise a problem that the high rotational speed of hard disks will make noise conspicuous and power consumption great. Although this problem can be solved if the initialization is performed in the silent mode, it is not sufficient for media where a higher drive speed is suitable, because the setting has to be changed each time an initialization is made. Particularly, the demand for power-saving becomes important in the case where a battery-powered information processor, such as notebook-sized type, laptop type, and other portable type information processors, has a limit to an energy resource.
In an optical disk system having interchangeability between different optical disks, there have hitherto been proposed a method of automatically discriminating disks and a method of canceling noise in image data which is reproduced at a variable rate. For example, Published Unexamined Patent Application No. 9-198780 discloses an optical system equipped with a method of automatically discriminating disks. In the method disclosed in the above-mentioned Published Unexamined Patent Application No. 9-198780, the cycle of an information signal reproduced from a disk is detected to discriminate a DVD and a CD. When it is higher than a reference value, the disk is judged to be a DVD. On the other hand, when it is lower than the reference value, the disk is judged to be a CD.
However, this method is capable of discriminating between a CD and a DVD, but cannot provide a drive speed corresponding to information recorded on the DVD. Thus, the method is not suitable for solving the aforementioned problem of noise and power consumption.
Furthermore, Published Unexamined Patent Application No. 10-210420 discloses a method of suitably canceling noise in image data reproduced at a variable rate. However, this method is not a method suitable for solving the aforementioned problem of noise and power consumption.